Middleware for PHP
PHP
Latest commit 29f6e8c May 21, 2015 @weierophinney weierophinney Merge branch 'hotfix/abandon'
Rebranded to zend-stratigility

README.md

Conduit

Abandoned! Or, rather, rebranded!

phly/conduit has moved to the zendframework organization as zend-stratigility (from Strata, meaning "layer," and "agility").

Please use that package instead, and contribute issues and pull requests against it I have closed issues and pull requests against phly/conduit at this time.

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Conduit is a port of Sencha Connect to PHP. It allows you to build applications out of middleware.

Installation and Requirements

Install this library using composer:

$ composer require phly/http phly/conduit

Conduit has the following dependencies (which are managed by Composer):

  • psr/http-message, which provides the interfaces specified in PSR-7, and type-hinted against in this package. In order to use Conduit, you will need an implementation of PSR-7; one such package is phly/http (and hence the reference to it in the install line above).
  • zendframework/zend-escaper, used by the FinalHandler for escaping error messages prior to passing them to the response.

You can provide your own request and response implementations if desired as long as they implement the PSR HTTP message interfaces.

Usage

Creating an application consists of 3 steps:

  • Create middleware or a middleware pipeline
  • Create a server, using the middleware
  • Instruct the server to listen for a request
use Phly\Conduit\MiddlewarePipe;
use Phly\Http\Server;

require __DIR__ . '/../vendor/autoload.php';

$app    = new MiddlewarePipe();
$server = Server::createServer($app,
  $_SERVER,
  $_GET,
  $_POST,
  $_COOKIE,
  $_FILES
);
$server->listen();

The above example is useless by itself until you pipe middleware into the application.

Middleware

What is middleware?

Middleware is code that exists between the request and response, and which can take the incoming request, perform actions based on it, and either complete the response or pass delegation on to the next middleware in the queue.

use Phly\Conduit\MiddlewarePipe;
use Phly\Http\Server;

require __DIR__ . '/../vendor/autoload.php';

$app    = new MiddlewarePipe();
$server = Server::createServer($app, $_SERVER, $_GET, $_POST, $_COOKIE, $_FILES);

// Landing page
$app->pipe('/', function ($req, $res, $next) {
    if ($req->getUri()->getPath() !== '/') {
        return $next($req, $res);
    }
    return $res->end('Hello world!');
});

// Another page
$app->pipe('/foo', function ($req, $res, $next) {
    return $res->end('FOO!');
});

$server->listen();

In the above example, we have two examples of middleware. The first is a landing page, and listens at the path /. If the path is an exact match, it completes the response. If it is not, it delegates to the next middleware in the stack. The second middleware matches on the path /foo -- meaning it will match /foo, /foo/, and any path beneath. In that case, it will complete the response with its own message. If no paths match at this point, a "final handler" is composed by default to report 404 status.

So, concisely put, middleware are PHP callables that accept a request and response object, and do something with it.

Middleware can decide more processing can be performed by calling the $next callable that is passed as the third argument. With this paradigm, you can build a workflow engine for handling requests -- for instance, you could have middleware perform the following:

  • Handle authentication details
  • Perform content negotiation
  • Perform HTTP negotiation
  • Route the path to a more appropriate, specific handler

Each middleware can itself be middleware, and can attach to specific paths -- allowing you to mix and match applications under a common domain. As an example, you could put API middleware next to middleware that serves its documentation, next to middleware that serves files, and segregate each by URI:

$app->pipe('/api', $apiMiddleware);
$app->pipe('/docs', $apiDocMiddleware);
$app->pipe('/files', $filesMiddleware);

The handlers in each middleware attached this way will see a URI with that path segment stripped -- allowing them to be developed separately and re-used under any path you wish.

Within Conduit, middleware can be:

  • Any PHP callable that accepts, minimally, a PSR-7 request and a response (in that order), and, optionally, a callable (for invoking the next middleware in the queue, if any).
  • An object implementing Phly\Conduit\MiddlewareInterface. Phly\Conduit\MiddlewarePipe implements this interface.

Error Handlers

To handle errors, you can write middleware that accepts exactly four arguments:

function ($error, $request, $response, $next) { }

Alternately, you can implement Phly\Conduit\ErrorMiddlewareInterface.

When using MiddlewarePipe, as the queue is executed, if $next() is called with an argument, or if an exception is thrown, middleware will iterate through the queue until the first such error handler is found. That error handler can either complete the request, or itself call $next(). Error handlers that call $next() SHOULD call it with the error it received itself, or with another error.

Error handlers are usually attached at the end of middleware, to prevent attempts at executing non-error-handling middleware, and to ensure they can intercept errors from any other handlers.

Creating Middleware

To create middleware, write a callable capable of receiving minimally a request and a response object, and optionally a callback to call the next in the chain. In your middleware, you can handle as much or as little of the request as you want -- including delegating to other middleware. If your middleware accepts a third argument, $next, if it is unable to complete the request, or allows further processing, it can call it to return handling to the parent middleware.

As an example, consider the following middleware which will use an external router to map the incoming request path to a handler; if unable to map the request, it returns processing to the next middleware.

function ($req, $res, $next) use ($router) {
    $path = $req->getUri()->getPath();

    // Route the path
    $route = $router->route($path);
    if (! $route) {
        return $next($req, $res);
    }

    $handler = $route->getHandler();
    return $handler($req, $res, $next);
}

Middleware written in this way can be any of the following:

  • Closures (as shown above)
  • Functions
  • Static class methods
  • PHP array callbacks (e.g., [ $dispatcher, 'dispatch' ], where $dispatcher is a class instance)
  • Invokable PHP objects (i.e., instances of classes implementing __invoke())
  • Objects implementing Phly\Conduit\MiddlewareInterface (including Phly\Conduit\MiddlewarePipe)

In all cases, if you wish to implement typehinting, the signature is:

function (
    Psr\Http\Message\ServerRequestInterface $request,
    Psr\Http\Message\ResponseInterface $response,
    callable $next = null
) {
}

The implementation Conduit offers also allows you to write specialized error handler middleware. The signature is the same as for normal middleware, except that it expects an additional argument prepended to the signature, $error. (Alternately, you can implement Phly\Conduit\ErrorMiddlewareInterface.) The signature is:

function (
    $error, // Can be any type
    Psr\Http\Message\ServerRequestInterface $request,
    Psr\Http\Message\ResponseInterface $response,
    callable $next
) {
}

Executing and composing middleware

The easiest way to execute middleware is to write closures and attach them to a Phly\Conduit\MiddlewarePipe instance. You can nest MiddlewarePipe instances to create groups of related middleware, and attach them using a base path so they only execute if that path is matched.

$api = new MiddlewarePipe();  // API middleware collection
$api->pipe(/* ... */);        // repeat as necessary

$app = new MiddlewarePipe();  // Middleware representing the application
$app->pipe('/api', $api);     // API middleware attached to the path "/api"

Another approach is to extend the Phly\Conduit\MiddlewarePipe class itself -- particularly if you want to allow attaching other middleware to your own middleware. In such a case, you will generally override the __invoke() method to perform any additional logic you have, and then call on the parent in order to iterate through your stack of middleware:

use Phly\Conduit\MiddlewarePipe;
use Psr\Http\Message\ServerRequestInterface as Request;
use Psr\Http\Message\ResponseInterface as Response;

class CustomMiddleware extends MiddlewarePipe
{
    public function __invoke(Request $request, Response $response, callable $next = null)
    {
        // perform some work...

        // delegate to parent
        parent::__invoke($request, $response, $next);

        // maybe do more work?
    }
}

Another approach using this method would be to override the constructor to add in specific middleware, perhaps using configuration provided. In this case, make sure to also call parent::__construct() to ensure the middleware queue is initialized; I recommend doing this as the first action of the method.

use Phly\Conduit\MiddlewarePipe;

class CustomMiddleware extends MiddlewarePipe
{
    public function __construct($configuration)
    {
        parent::__construct();

        // do something with configuration ...

        // attach some middleware ...

        $this->pipe(/* some middleware */);
    }
}

These approaches are particularly suited for cases where you may want to implement a specific workflow for an application segment using existing middleware, but do not necessarily want that middleware applied to all requests in the application.

API

The following make up the primary API of Conduit.

Middleware

Phly\Conduit\MiddlewarePipe is the primary application interface, and has been discussed previously. Its API is:

class MiddlewarePipe implements MiddlewareInterface
{
    public function pipe($path, $middleware = null);
    public function __invoke(
        Psr\Http\Message\ServerRequestInterface $request = null,
        Psr\Http\Message\ResponseInterface $response = null,
        callable $out = null
    );
}

pipe() takes up to two arguments. If only one argument is provided, $middleware will be assigned that value, and $path will be re-assigned to the value /; this is an indication that the $middleware should be invoked for any path. If $path is provided, the $middleware will only be executed for that path and any subpaths.

Middleware is executed in the order in which it is piped to the MiddlewarePipe instance.

__invoke() is itself middleware. If $out is not provided, an instance of Phly\Conduit\FinalHandler will be created, and used in the event that the pipe stack is exhausted. The callable should use the same signature as Next():

function (
    Psr\Http\Message\ServerRequestInterface $request,
    Psr\Http\Message\ResponseInterface $response,
    $err = null
) {
}

Internally, MiddlewarePipe creates an instance of Phly\Conduit\Next, feeding it its queue, executes it, and returns a response.

Next

Phly\Conduit\Next is primarily an implementation detail of middleware, and exists to allow delegating to middleware registered later in the stack.

Because Psr\Http\Message's interfaces are immutable, if you make changes to your Request and/or Response instances, you will have new instances, and will need to make these known to the next middleware in the chain. Next expects these arguments for every invocation. Additionally, if an error condition has occurred, you may pass an optional third argument, $err, representing the error condition.

class Next
{
    public function __invoke(
        Psr\Http\Message\ServerRequestInterface $request,
        Psr\Http\Message\ResponseInterface $response,
        $err = null
    );
}

You should always either capture or return the return value of $next() when calling it in your application. The expected return value is a response instance, but if it is not, you may want to return the response provided to you.

As examples:

Providing an altered request:

function ($request, $response, $next) use ($bodyParser)
{
    $bodyParams = $bodyParser($request);
    return $next(
        $request->withBodyParams($bodyParams), // Next will pass the new
        $response                              // request instance
    );
}

Providing an altered response:

function ($request, $response, $next)
{
    $updated = $response->addHeader('Cache-Control', [
        'public',
        'max-age=18600',
        's-maxage=18600',
    ]);
    return $next(
        $request,
        $updated
    );
}

Providing both an altered request and response:

function ($request, $response, $next) use ($bodyParser)
{
    $updated = $response->addHeader('Cache-Control', [
        'public',
        'max-age=18600',
        's-maxage=18600',
    ]);
    return $next(
        $request->withBodyParams($bodyParser($request)),
        $updated
    );
}

Returning a response to complete the request

If you have no changes to the response, and do not want further middleware in the pipeline to execute, do not call $next() and simply return from your middleware. However, it's almost always better and more predictable to return the response instance, as this will ensure it propagates back up to all callers.

function ($request, $response, $next)
{
    $response = $response->addHeader('Cache-Control', [
        'public',
        'max-age=18600',
        's-maxage=18600',
    ]);
    return $response;
}

One caveat: if you are in a nested middleware or not the first in the stack, all parent and/or previous middleware must also call return $next(/* ... */) for this to work correctly.

As such, I recommend always returning $next() when invoking it in your middleware:

return $next(/* ... */);

And, if not calling $next(), returning the response instance:

return $response

Raising an error condition

To raise an error condition, pass a non-null value as the third argument to $next():

function ($request, $response, $next)
{
    try {
        // try some operation...
    } catch (Exception $e) {
        return $next($request, $response, $e); // Next registered error middleware will be invoked
    }
}

FinalHandler

Phly\Conduit\FinalHandler is a default implementation of middleware to execute when the stack exhausts itself. It expects three arguments when invoked: a request instance, a response instance, and an error condition (or null for no error). It returns a response.

FinalHandler allows an optional argument during instantiation, $options, an array of options with which to configure itself. These options currently include:

  • env, the application environment. If set to "production", no stack traces will be provided.
  • onerror, a callable to execute if an error is passed when FinalHandler is invoked. The callable is invoked with the error (which will be null in the absence of an error), the request, and the response, in that order.

HTTP Messages

Phly\Conduit\Http\Request

Phly\Conduit\Http\Request acts as a decorator for a Psr\Http\Message\ServerRequestInterface instance. The primary reason is to allow composing middleware such that you always have access to the original request instance.

As an example, consider the following:

$app1 = new Middleware();
$app1->pipe('/foo', $fooCallback);

$app2 = new Middleware();
$app2->pipe('/root', $app1);

$server = Server::createServer($app2 /* ... */);

In the above, if the URI of the original incoming request is /root/foo, what $fooCallback will receive is a URI with a past consisting of only /foo. This practice ensures that middleware can be nested safely and resolve regardless of the nesting level.

If you want access to the full URI — for instance, to construct a fully qualified URI to your current middleware — Phly\Conduit\Http\Request contains a method, getOriginalRequest(), which will always return the original request provided to the application:

function ($request, $response, $next)
{
    $location = $request->getOriginalRequest()->getUri()->getPath() . '/[:id]';
    $response = $response->setHeader('Location', $location);
    $response = $response->setStatus(302);
    return $response;
}

Phly\Conduit\Http\Response

Phly\Conduit\Http\Response acts as a decorator for a Psr\Http\Message\ResponseInterface instance, and also implements Phly\Conduit\Http\ResponseInterface, which provides the following convenience methods:

  • write(), which proxies to the write() method of the composed response stream.
  • end(), which marks the response as complete; it can take an optional argument, which, when provided, will be passed to the write() method. Once end() has been called, the response is immutable.
  • isComplete() indicates whether or not end() has been called.

Additionally, it provides access to the original response created by the server via the method getOriginalResponse().